1. Field of the Invention
The present invention relates to a structure for supporting a lower suspension arm of a vehicle suspension on the chassis of a vehicle by means of a bracket.
2. Description of the Related Art
In general, a lower suspension arm of a vehicle suspension extends in the lateral direction of the chassis and is pivotally supported at its laterally inner end on a portion of the chassis. It is well known that the rigidity of the structure for supporting the lower suspension arm on the chassis significantly affects the control stability of the vehicle. More specifically, the control stability of the vehicle is appreciably improved by enhancing the rigidity of the structures through which the lower suspension arms associated with steerable front wheels are supported on the chassis. In order to improve the control stability, therefore, various types of lower suspension arm supporting structures have been proposed heretofore.
FIGS. 6 and 7 show an example of a known lower suspension arm supporting structure. In this structure, a lower suspension arm 10 of a front suspension has an L-like form composed of a front portion adjacent to the front end of a chassis and a rear portion adjacent to the rear end of the chassis, the front and rear portions being secured to the chassis independently of each other. For the details of this structure, a reference is made to "TOYOTA COROLLA/COROLLA LEVIN New Model Instruction Manual", pp 4-100, issued from the Service Dept. of Toyota Motor Co., Ltd. on May 12, 1983.
In this known structure, a connecting portion 12 in the front portion of the lower suspension arm 10 is pivotally connected through a bush 14 and a bolt 16 to a side member 13 which constitutes one of the structural members of the chassis, while a connecting portion 18 on the rear portion of the lower suspension arm 10 is pivotally connected through a bush 26 to a bracket 24 which is connected by bolts 22 to a dash panel cross-member 20 which also is a structural member of the chassis. In these Figures, an arrow FR represents the forward direction of the chassis, while an arrow IN indicates the laterally inward direction of the chassis. The upward direction is indicated by an arrow UP. Thus, the longitudinal direction, lateral direction and vertical direction with respect to the chassis are defined by those arrows FR, IN and UP, respectively. The same arrow symbols appearing throughout the drawings attached to this specification indicate the same directions.
This structure can have a reduced size since the lower suspension arm 10 serves also as a strut bar, yet exhibits a high rigidity because the lower suspension arm is supported at both of its ends with a sufficiently large supporting span.
The bracket 24 extends laterally across the lower suspension arm 10 and is connected at both of its lateral ends to the dash panel cross-member 20. Both connecting points are positioned at a level above the axis CL about which the lower suspension arm 10 swings. In consequence, the force applied to the lower suspension arm 10 in the longitudinal direction of the chassis acts on the bracket 24 at a point which is spaced downwardly from the points at which the bracket 24 is connected to the dash panel cross-member 20, with the result that a moment of force is produced tending to displace or deform the bracket 24, as indicated by arrows in FIG. 6.
In order to obviate this problem, Japanese Utility Model No. 23188/1981 entitled "Construction for Securing Suspension Arm in Front Suspension" proposes an improved structure for supporting a lower suspension arm. As shown in FIG. 8, this proposed supporting structure comprises a lower suspension arm supporting bracket 28 which extends in the forward and backward direction of the chassis, and has a lower suspension arm supporting portion which is closed at its rear end. The bracket 28 has a front end portion which is connected to the underside of a front side member 30 and a rear end portion which is connected to the lower end surface of a cross-member 32 and which is positioned at a level vertically above the level of the front side member 30. Since the bracket 28 has an enhanced rigidity, the force transmitted through the lower suspension arm and acting on a second bracket (not shown) in the longitudinal direction of the chassis causes only a small displacement of the bracket 28. Unfortunately, however, this improved structure cannot reduce the displacement of the bracket 28 to an acceptable level, because a moment of force is also produced in this structure due to the fact that the points at which the bracket 28 is connected to the chassis are located above the swinging axis CL of the lower suspension arm.
Another improved structure is proposed in Japanese Unexamined Utility Model Publication No. 157486/1985 entitled "Construction of Automotive Body". In this structure, a front side member on which the lower suspension arm is supported engages with a steering support cross-member through a rigid member. According to this structure, the displacement of the front side member in the lateral direction of the chassis is suppressed so that the lower suspension arm supporting structure exhibits an extremely high rigidity against lateral force. However, this structure is not arranged to exhibit rigidity of a level which is large enough to suppress the displacement of the bracket.